1. Field of the Invention
The present invention relates to a structural body accommodating electronic components, and more particularly to a sealing structure applied to a housing chamber in which electronic components are accommodated and also applied to a cooling passage formed in a structural body to cool the electronic component.
2. Description of the Related Art
Electronic components and electronic units or assemblies accommodating numerous electronic components tend to generate a great amount of heat. For example, an automotive vehicle equipped with a hybrid power plant (i.e., a combined electric motor/internal combustion engine) or an electric vehicle is subjected to a significant amount of heat generated from electronic components constituting an inverter device or a converter device. The electronic components are generally accommodated in a structural body including a metallic housing body. Furthermore, the structural body usually includes a cooling passage in which coolant flows and heat dissipating fins to cool the heated electronic components.
FIG. 5 shows a conventional structural body configured to accommodate electronic components. A power control unit 100 is a device that can control electrical power supplied to a hybrid power plant. The power control unit 100 includes a boosting converter section 102 and a driving inverter section 104 mounted on the boosting converter section 102. The boosting converter section 102 boosts a DC voltage supplied from a battery. The driving inverter section 104 converts a boosted DC voltage into an AC voltage and supplies the converted AC voltage to the electric motor.
The driving inverter section 104 includes electronic components (not shown) constituting an inverter device and an inverter housing body 106 accommodating the electronic components. The inverter housing body 106 has a housing chamber in which the electronic components are installed. The electronic components are fixed to the housing body 106 by means of bolts or the like. Similar to the inverter section 104, the boosting converter section 102 includes a converter housing body 108 having a housing chamber in which electronic components are installed.
The housing chamber of the inverter housing body 106 and the housing chamber of the converter housing body 108 can be connected via a communicating passage 110 when the boosting converter section 102 and the driving inverter section 104 are assembled together. The communicating passage 110 provides a space in which bus bars and a wiring harness can extend to connect the electronic components of the inverter device and the electronic components of the converter device. The bus bars and the wiring harness can supply a boosted electrical power from the converter to the inverter. For example, there is a possibility of a high voltage of 600 V being applied to the bus bars and the wiring harness. Accordingly, to eliminate leakage of the electrical power, the communicating passage 110 must have sufficient water-proof properties.
Furthermore, the power control unit 100 includes a cooling passage 112 in which coolant flows to cool the electronic components installed in the housing chambers. The cooling passage 112 consists of two side walls, one of which is formed on the inverter housing body 106 and the other is on the converter housing body 108. More specifically, joining surfaces 120 of the housing bodies 106 and 108 are partly recessed into a predetermined groove shape to form the side walls of the cooling passage 112. The cooling passage 112 can be formed when the inverter housing body 106 and the converter housing body 108 are coupled or assembled at their joining surfaces 120. In general, cooling water flows as the coolant in the cooling passage 112 and circulates in a radiator installed in an automotive vehicle.
As described above, the joining surfaces 120 are defined as boundary surfaces of the housing bodies 106 and 108 in a coupled or assembled condition. The joining surfaces 120 include a communicating passage area 114 where the communicating passage 110 is provided and a liquid passage area 116 where the cooling passage is provided. As described above, the communicating passage 110 formed in the communicating passage area 114 must have sufficient water-proof properties. Meanwhile, the cooling water flows in the cooling passage provided in the liquid passage area 116. Thus, the communicating passage area 114 requiring water-proof properties and the liquid passage area 116 including the cooling passage must be independently sealed.
The communicating passage area 114 must be sealed considering not only the cooling water entering from the liquid passage area 116 but also the external water entering from the outside of the structural body. On the other hand, the liquid passage area 116 must be sealed considering not only the cooling water flowing into the communicating passage area 114 but also the cooling water leaking out of the housing body. Preventing the cooling water from leaking out of the structural body facilitates realizing a reliable cooling system that can stably maintain a sufficient amount of cooling water circulating to cool the electronic components.
To this end, a sealing surface having a predetermined surface roughness is formed at a portion indicated by an alternate long and short dash line in FIG. 5. The sealing surface can independently seal the communicating passage area 114 and the liquid passage area 116 at the joining surfaces 120 of two housing bodies 106 and 108. More specifically, the sealing surface is formed on the joining surface(s) 120 of the housing bodies to independently surround the communicating passage area 114 and the liquid passage area 116.
A liquid gasket agent containing silicone rubber and other components, so-called FIPG (Formed in place gasket), is conventionally coated or applied on the sealing surfaces before the housing bodies are coupled. FIPG (i.e., liquid gasket agent) can enhance sealing properties of an inner clearance between the communicating passage area 114 and the liquid passage area 116. When a sufficient amount of FIPG hardens between the sealing surfaces of coupled housing bodies 106 and 108, FIPG can eliminate the cooling water leaking out of the liquid passage area 116 and the water entering from the outside of the structural body. Thus, no water can enter into the communicating passage area 114. Furthermore, FIPG can eliminate the cooling water leaking out of the liquid passage area 116 to the outside.
However, in the conventional electronic component housing structural body, various problems occur due to the use of FIPG that can assure sealing properties. More specifically, in manufacturing processes, workers must carefully and uniformly apply a predetermined amount of FIPG on the sealing surface(s). Applying the FIPG on the sealing surface(s) in the above-described manner takes a long time and requires an increased manufacturing lead time to accomplish the coupling of two housing bodies. Furthermore, applying the FIPG on the sealing surface(s) places a heavy burden on workers and requires careful management with respect to the applying amount.
Furthermore, according to the electronic component housing structural body such as the above-described conventional power control unit, the coupled housing bodies must be separated again if any damage or problem occurs inside the structural body so that the housing body including a damaged or problematic electronic component can be removed and replaced as a unit. However, the housing bodies are tightly fixed together by the FIPG that has already hardened. Thus, separation of the housing bodies is necessarily accompanied by troublesome work for removing or peeling the hardened FIPG off the sealing surfaces of the housing bodies. Hence, the sealing surfaces may be scratched or damaged if the work is done roughly. For example, a worker may use a screwdriver to forcibly separate the connected housing bodies, and may use a scraper to peel the FIPG off the sealing surfaces. In such a case, the sealing surfaces possibly have scratches and water leakage may occur due to the scratches. Thus, the housing bodies are no longer suitable to newly apply the FIPG on their sealing surfaces to connect the housing bodies again. Therefore, the power control unit, i.e., the electronic component housing structural body, must be removed as a unit or assembly to be replaced at that time.
Furthermore, an O-ring serving as a member constituting an inverter device proposed in Japanese Patent Laid-open Application No. Hei 10-213366 cannot be used to seal the joining surfaces of the above-described electronic component housing structural body. At least three O-rings must be disposed on the sealing surface(s) to independently seal the communicating passage area and the liquid passage area from the outside at the fitting faces of the housing bodies. The total number of constituent components thus increases, and the manufacturing cost also increases. Furthermore, disposing three O-rings on the sealing surface(s) is not practical in view of manufacturing workability.